The formation of polymers by anionic polymerization is well known in the art. These polymers are typically achieved by the formation of a living polymer that reacts with monomeric segments. Completion of this polymerization process is generally achieved by terminating this living polymer. In other words, the living end is reacted with a terminating agent that quenches the polymerization process. Many terminating agents, which also include coupling or linking agents, are known in the art.
When conducting polymerizations on a commercial basis, it is important to utilize process conditions and components that will allow the molecular weight of the end products to be narrowly and reproducibly defined. The characteristics of a given polymer and its usefulness are dependent, among other things, upon its molecular weight. Hence, it is desirable to be able to predict with some certainty the molecular weight of the end product of the polymerization. When the molecular weight is not narrowly definable, or is not reproducible on a systematic basis, the process is not commercially viable. Living anionic polymerization typically affords the ability to control not only molecular weight, but also to obtain a relatively narrow molecular weight distribution.
In the art, it is desirable to produce vulcanizates exhibiting reduced hysteresis loss characteristics. When these vulcanizates are fabricated into articles such as tires, power belts, and the like, they show an increase in rebound, a decrease in rolling resistance, and will have less heat build-up when mechanical stresses are applied.
It is believed that a major source of hysteretic power loss is caused by the section of the polymer chain from the last cross link of the vulcanizate to the end of the polymer chain. This free end cannot be involved in an efficient, classically recoverable process; and as a result, any energy transmitted to this section of the cured vulcanizate is lost as heat. It is known in the art that this type of mechanism can be reduced by preparing higher molecular weight polymers that will have fewer end groups. However, this procedure is not useful because rubber processability when combined with compounding ingredients decreases rapidly during mixing and shaping operations.
It is also known in the art to reduce hysteresis loss by providing the end of the polymeric chain with a functional unit that will serve to anchor the free end and reduce hysteresis loss. For example, U.S. Pat. No. 5,552,473 to Lawson et al. teaches polymers initiated with one functional group and terminated with a second functional group. As a result, an elastomer is produced having greater affinity for compounding materials, such as carbon black, thereby reducing hysteresis loss. Others have provided the end of elastomers that are useful in making tires with a number of end-functionalities. For example, U.S. Pat. No. 5,015,692 teaches polymer functionalization through terminating reactions with nitro compounds, phosphoryl chloride compounds, and amino silane compounds. In a similar fashion, U.S. Pat. No. 5,128,416 teaches end-functionalization through terminating reactions with phosphoryl chloride, amino silane, acrylamides, or aminovinyl silane compounds in combination with conventional silicon or tin coupling compounds. Still further, U.S. Pat. No. 4,730,025 teaches a process whereby moving polymers are reacted with certain terminating agents resulting in the formation of a reactive end-group that can subsequently be reacted with the backbone of other polymer chains. The functionalizing agents include tetraalkylthiurane disulfides, xanthates, and certain compounds containing tetrachlorocyclopentadiene radicals.
Because the reduction in hysteresis of rubber vulcanizates remains a goal of the tire industry, there is a need for new and useful functionalized polymers capable of exhibiting these properties. Also, functionalized polymers can be used in a variety of other applications. For example, certain reactive functional groups can serve as a location within a polymer where grafting and coupling reactions can take place.